Research On The Liquid-phase Conversion Of Biomass-based Carbohvdrates Into5-hydroxymethylfurfural

As an important platform chemical and feedstock to produce various chemicals and liquid fuels,5-hydroxymethylfuraldehyde (HMF) can be produced by the conversion of biomass carbohydrates. Due to the limited knowledge of biomass decomposition mechanism in solvents, its widespread utilization is restricted. Supported by National Natural Science Foundation, a systematic study on biomass-based carbohydrates (hexose and cellulose) decomposition in solvents is presented in this thesis.The most typical hexose in biomass-glucose, was selected as the model compound to study the mechanism of monosaccharide conversion for HMF production. A parallel reaction model, in which the main reaction was to produce HMF and levulinic acid (LA), the side reaction was to yield humin, was proposed. Reaction kinetics of glucose decomposition in water, dimethylsulfoxide (DMSO), and DMSO-water(1:1) mixture were investigated at100-200℃. The kinetic parameters were fitted using Matlab software. The results revealed that DMSO not only promoted the isomerization of glucose to fructose, but also enhanced the yield of humin. The generated HMF quickly extracted by DMSO decreased the encounter probability of HMF and water, which further restrained the reaction leading to LA. Moreover, galactose was also detected during glucose decomposition in DMSO, indicating that other isomerization paths existed in this process. The experiments of a Fourier transform infrared spectrometry (FTIR) and elemental analysis proved that the solid product humin was resulted from the repolymerization of glucose and HMF.In order to further research on the mechanism of hexose isomerization, the liquid-phase decomposition of three main hexoses in biomass-galactose, mannose and glucose, was proposed, which showed the products distribution was similar to each other. The HMF yield for glucose and mannose was slightly higher than that for galactose, which was attributed to the higher reactivity of fructose than tagatose. In addition, higher LA yield was detected in galactose decomposition. The activation energies of side reactions showed that galactose and mannose were more easily to yield humin, which was consistent with the product selectivity. The generate path of humin was the repolymerization of monosaccharide and HMF, which was also proved by the results of FTIR and elemental analysis.Microcrystalline cellulose, the main hexoses polysaccharide in lignocellulosic biomass, was used to study the correlation of cellulose hydrolysis, glucose isomerization and degradation of intermediate. The experiment was proceeded in a pressure reactor to study the product distribution and optimize the reaction conditions. The major products were furans, alcohols, esters and sugars, as well as a little acid and pyridine. Higher methanol-soluble products yield could be achieved when it was closed to the critical condition. There existed an optimal reaction time for cellulose alcoholysis. Before this time, raw material transformation was incomplete, while after that, the methanol-soluble products would profound decompose into small molecular gaseous products. Moreover, a lower ratio of raw material and solvent could promote methanol-soluble products yield and reduce the coke formation.